E621

E621 may refer to:

Rail locomotives

 * FS Class E.621, a 1947 Italian model
 * E621, a 2013 Japanese E6 Series Shinkansen railcar

Other uses

 * Monosodium glutamate, a food flavour enhancer (labelled E621 in the EU)
 * e621.net, a booru-style furry fandom imageboard owned by the CEO of Bad Dragon